Fuel cell stacks are electrochemical devices that produce water and an electrical potential from a fuel, such as a proton source, and an oxidant. Many conventional fuel cell stacks utilize hydrogen gas as the proton source and oxygen gas, air, or oxygen-enriched air as the oxidant. Fuel cell stacks typically include many fuels cells that are fluidly and electrically coupled together between common end plates. Each fuel cell includes an anode region and a cathode region that are separated by an electrolytic barrier. In some fuel cells, the electrolytic barrier takes the form of an electrolytic membrane. Hydrogen gas is delivered to the anode region, and oxygen gas is delivered to the cathode region. Protons from the hydrogen gas are drawn through the electrolytic barrier to the cathode region, where water is formed. While protons may pass through the electrolytic barrier, electrons cannot. Instead, the electrons that are liberated from hydrogen gas travel through an external circuit to form an electric current.
Fuel cell systems may be designed to be the primary and/or backup power source for an energy-consuming assembly that includes one or more energy-consuming devices. When implemented as a backup, or auxiliary, power source for an energy-consuming assembly, the fuel cell system is utilized during times when the primary power source is unable or unavailable to satisfy some or all of the energy demand, or applied load, of the energy-consuming assembly.
The electrolytic membranes of some fuel cell systems, such as proton exchange membranes (PEM), or solid polymer fuel cell systems, generally need a proper level of hydration to allow the electrolytic membranes to function efficiently for generation of electrical output. During generation of power by a fuel cell system, water for membrane hydration is generated by electrochemical reaction. However, during periods of inactivity, which are common for fuel cell systems that are utilized as an auxiliary (i.e. backup) power supply, the electrolytic membranes have a tendency to dry out as their period of inactivity increases. As a result, the ability of the fuel cell system to reliably and efficiently provide power when needed may be reduced substantially. One approach to maintaining hydration is to connect the fuel cell system to an artificial, or “dummy,” load, such as one or more resistors or light assemblies, and then to operate the fuel cell system periodically to supply power to the artificial load. This load-applying structure is referred to as an artificial load because it is present primarily to enable the fuel cell system to generate an electrical output by satisfying the applied load. However, the artificial load increases the size, weight and/or expense of the fuel cell system. Furthermore, other than providing maintenance, powering the artificial load wastes electrical output—and thus fuel—and may generate substantial heat in or near the fuel cell system. Accordingly, new approaches are needed for maintaining the readiness of fuel cell systems serving as backup power sources.